Finally received my replacement HE-500 (first unit had L/R imbalance). Tested the drivers on my Fluke meter and got 44.8ohm on one side and 45.1ohm on the other. Replacement took 3 weeks to arrive after they received the bad set, so not the most responsive customer service.

But the sound quality is fantastic out of the box, currently doing some burn-in. Unlike some I do notice an improvement in SQ for orthos after 100+ hours of run-in. I'm expecting the bass to be a little tighter/better controlled and a slight edge smoothed out from the treble.

These are more power hungry than I had expected, but my Pioneer SX-D7000 is having no problem driving them.

Finally received my replacement HE-500 (first unit had L/R imbalance). Tested the drivers on my Fluke meter and got 44.8ohm on one side and 45.1ohm on the other. Replacement took 3 weeks to arrive after they received the bad set, so not the most responsive customer service.

But the sound quality is fantastic out of the box, currently doing some burn-in. Unlike some I do notice an improvement in SQ for orthos after 100+ hours of run-in. I'm expecting the bass to be a little tighter/better controlled and a slight edge smoothed out from the treble.

These are more power hungry than I had expected, but my Pioneer SX-D7000 is having no problem driving them.

I'm curious, do you have the measurement values from the pair you sent back?

After reading this thread I measured my HE500 and found L=24ohm / R=35ohm

Thank you Murray for doing that math. This is why I was curious of Argybargy’s measurements, he seemed immediately aware of a problem, but this imbalance never jumped out at me. On the other hand, I’ve never really warmed up to these HE500’s either. Maybe they are capable of much more had the drivers been better matched.

Out of curiosity I measured all my other speakers in the house, Klipsch, Meadowlark, Celestion, AKG K340 & LCD-2’s and the worst discrepancy I found was only 0.1 Ohm. This makes me wonder if these HE500’s shouldn't be better matched at this price point?

Thank you Murray for doing that math. This is why I was curious of Argybargy’s measurements, he seemed immediately aware of a problem, but this imbalance never jumped out at me. On the other hand, I’ve never really warmed up to these HE500’s either. Maybe they are capable of much more had the drivers been better matched.

Out of curiosity I measured all my other speakers in the house, Klipsch, Meadowlark, Celestion, AKG K340 & LCD-2’s and the worst discrepancy I found was only 0.1 Ohm. This makes me wonder if these HE500’s shouldn't be better matched at this price point?

The orthodynamic drivers are apparently almost entirely resistive, without much inductance or capacitance. This means that the measured DC resistance (in ohms) will be close to the AC impedance at audio frequencies.

On the other hand, most loudspeakers have strong resonant driver peaks as well as crossover networks that result in a very changeable AC impedance over the audio band that will differ from the measured DC resistance.

If you look at some of the Headroom graphs for dynamic headphones you will see that they also can have a wide impedance variation over the audio band.

For this reason the orthodynamic drivers, being resistive only, can be calculated in such a simple manner. I wouldn't have attempted a simple answer (as above) for dynamic drivers or loudpeakers - each case would be individually distinct. Measuring actual AC impedance requires a more complicated setup to get readings across the audible spectrum.

In your case, you may be lucky enough to just require a tweak of the "balance" control (if you have one) to correct for the difference. Do you hear the image shifted to one side? If so, try swapping the 'phones around to see if the audible offset switches sides.

I did not measure the first defective set since it was immediately obvious. I had to turn the balance knob about 75% to one side to equalize.

The replacement set after almost 100 hours of burn in measures 46.1ohm on the left and 46.6ohm on the right. I can actually hear the 1% difference which was why I measured again. I also thought it was my imagination that after some burn-in they were slightly harder to drive (requiring a touch more power) but the impedance was up by 2% which was what I was hearing.

They are now smoother and the slightly edgy treble is gone; for a while the extended full-bodied bass had alarmingly lightened up, but now it is back. Hopefully they'll stabilize in the next 50 hours.

Subscribed. I was thinking about "upgrading" to the HE-500's after returning my HE-400's. After looking inside the HE-400's I get a very queasy feeling about everything about this company. I am, however, hoping that the HE-500's are better with respect to internal build quality and overall QC. Your post gives me pause...

In 1st batch (shipping on Jan, 2012) we got about 15% customers report the issue of one side driver not working. We did some research on defective drivers, and noticed poor contact between metal trace and frame. We reinforce the contact, then problem solved. We run-in the fixed drivers for 100+ hrs and don't have the problem again. We will keep run-in the fixed drivers until 200+ hrs. Hopefully we will eluminate the problem from 2nd batch.

Which I'm fairly sure they did, many of us have since then received the 2nd batch HE-400's, and all except 1 person have had zero issues.

damn, I was wanting to get a pair of these. I still think I'm going to get a pair. If I dont notice any difference in volumes between the 2 driveers, should I still get a multimeter to measure them for any differences?

damn, I was wanting to get a pair of these. I still think I'm going to get a pair. If I dont notice any difference in volumes between the 2 driveers, should I still get a multimeter to measure them for any differences?

I wouldn't sweat it unless you actually hear something amiss. I just got HE-500's and played Stereophile's Test CD to check out pink noise, channel balance and test tones with my own ears and everything sounds absolutely fine. It's like that old adage... "if it smells good, eat it".